The present analysis suggests that the electricity cost of residential SOFC cogeneration systems can achieve 28-23 JPY/kWh, while middle/large SOFC combined cycle systems have a further cost reduction potential to reduce the electricity cost to ca. 14 JPY/kWh. Since the rate of renewable energy in the future electricity mix of Japan will be increased significantly, the structure of the future electricity mix of Japan will also change drastically. Given the situation, the role of SOFC systems and sharpening of their competitive edge were discussed, i.e., on the basis of the technology scenarios of residential and middle/large SOFC systems, technological issues for developing SOFC systems were considered using a sensitivity analysis with clarifying the conditions of widespread use of SOFC systems and their roles as base load power source, adjustor of the fluctuation of electricity in grids due to a large amount of the induction of renewable energy, and hydrogen production and storage system.